Laser beams are finding wide use in various fields such as optical office equipments and video devices, besides fields such as laser markers, laser trimmers and so forth. When a laser beam is used, it is necessary to properly position the laser beam, i.e., to effect deflection and scanning of laser beam. To this end, hitherto, laser scanner devices of galvanometer-type have been used popularly.
A galvanometer-type laser scanner device has, as shown in Japanese Patent Unexamined Publication No. 53-143910 for example, a mirror attached to the rotor shaft of an electric motor having a stator and a rotor capable of performing a limited rotation. The scanner device also has a position sensor of electrostatic capacitance type arranged around the rotor shaft of the motor, and output from this sensor is fed back to the instruction signal given to the motor, thereby to position the mirror.
This known laser scanner device, however, has suffered from the following disadvantages:
(1) A positional drift of 600 .mu.rad/.degree.C. or so is caused by a change in the ambient temperature.
(2) Response speed is low because the drive relies upon magnetic force. In particular, response speed is low at start-up of the motor (start-up time 3 to 4 msec).
Some of the known laser scanner devices of the type described above employ, as the rotation angle sensor for positioning the mirror, a low-inertia type device in which an electrostatic capacitance type sensor b is arranged to surround the rotation shaft a of the mirror. This type of rotation angle sensor is superior in that the rotation angle is sensed with a high resolution of 0.005.degree. or so, but undesirably exhibits a large temperature drift of 0.03.degree./.degree.C. or so. FIG. 2 shows another known rotation angle sensor for positioning the mirror, in which a light-emitting element d and a light-receiving element e are arranged spaced apart from the mirror rotation shaft c, so that the angular displacement of the shaft c is sensed by the light-receiving element e. This type of rotation angle sensor also exhibits high resolution and low inertia, but suffers from impractically narrow sensing coverage and inferior linearity.